Speedometer accuracy?
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Speedometer accuracy?
My 67 SB with 240 seems to consistently read about 5 mph faster than actual at least as indicated by the roadside speed minders. When buying new tires I made it a point to get tires as close to the original specs as possible. How is this corrected? Does this tend to give a higher or lower mpg than actual?
Lead Driver
Joined: Jul 2011
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From: On the Edge of the Desert
Speedometer reading fast will give you a higher mpg reading that is false.
To correct the issue, you need to change the speedometer driven gear on the end of the speedometer cable in the tail housing of the trans. Very easy and quick to do.
First you need to pull it out and count how many teeth you have on it now. Use a 3/8" wrench to free the locking tab then just give it a tug and it'll come right out. Count how many teeth there are and get one with one more from your Ford dealer they're cheap. Use a little 1/8 inch screwdriver to pop the clip off the gear. Pull gear off cable, and put it back together reversing these instructions.
One tooth should fix your problem, if not and it still reads a bit fast, you can add one more tooth and try again.
To correct the issue, you need to change the speedometer driven gear on the end of the speedometer cable in the tail housing of the trans. Very easy and quick to do.
First you need to pull it out and count how many teeth you have on it now. Use a 3/8" wrench to free the locking tab then just give it a tug and it'll come right out. Count how many teeth there are and get one with one more from your Ford dealer they're cheap. Use a little 1/8 inch screwdriver to pop the clip off the gear. Pull gear off cable, and put it back together reversing these instructions.
One tooth should fix your problem, if not and it still reads a bit fast, you can add one more tooth and try again.
Lead Driver
Joined: Apr 2011
Posts: 6,399
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From: El Dorado, Arkansas
Ford speedometer drive gears (the gear on the output shaft of the transmission) comes in 6, 7 and 8-tooth counts.
The driven gear (on the end of the speedometer cable going into the tail housing of the transmission) comes in 16-21 tooth counts.
Each tooth change of the driven gear is (generally) worth 3.375 MPH in change to the speedometer reading.
If you calculate the number of driven gear teeth needed and come up with something other than a whole number --18.4 just for example, round down and use an 18-tooth driven gear. If the number, just for example, was 18.7, round up and use a 19-tooth driven gear.
Speedometer Calibration Program - Method 1
Tire Diameter Calculator
Speedometer drive gear help needed - Ford Mustang Forums
The driven gear (on the end of the speedometer cable going into the tail housing of the transmission) comes in 16-21 tooth counts.
Each tooth change of the driven gear is (generally) worth 3.375 MPH in change to the speedometer reading.
If you calculate the number of driven gear teeth needed and come up with something other than a whole number --18.4 just for example, round down and use an 18-tooth driven gear. If the number, just for example, was 18.7, round up and use a 19-tooth driven gear.
Speedometer Calibration Program - Method 1
Tire Diameter Calculator
Speedometer drive gear help needed - Ford Mustang Forums
Lead Driver
Joined: Jul 2011
Posts: 8,679
Likes: 191
From: On the Edge of the Desert
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